The prior art has taught the use of printer-robot spraying devices controlled by a processing program for sequentially coating workpieces, such as the unfinished bodies of motor-vehicles. The processing program controlling the painter-robot contains control-information responsive to a plurality of individual paint impact points disposed on the workpiece which are approached by the painter-robot during the coating process. The control-information includes not only movement-control data but also information regarding the amount of paint required and, if air-operated spray-guns are used, information regarding the quantities of atomizing air and controlling air required. Additionally, information regarding specific signal/response delay-times of the various control elements, e.g., paint flow valves, is stored so that the process program may control the switching on and off of the spray-gun paint needle valve and also the particular device for metering the quantity of paint required. In this manner, the signal/response delay-times for opening and closing the paint needle-valve and for the switching times of other paint flow valves are initially adjusted to accurately maintain the program control signals ready for instantaneous change in response to the operating conditions during movement of the robot relative to the predetermined locations on the workpiece. In other words, because of the unavoidable signal/response time delays, switch-on commands must be given before the painter-robot reaches a particular paint impact point. Similarly, switch-off commands must be given when the painter-robot is still at a location which is to be coated.
With any given response behavior of the spraying device, the signal/response time delay information required for the program can be easily determined. However, the delay information stored in the process program no longer agrees with the actual conditions if the response behavior of the spraying device changes in the course of time. These response behavior changes are often unavoidable for various reasons, e.g., changes in friction or wear of the moving parts in the spraying device, a replaced spraying device, parts changes, etc. For these reasons, the quality of the coating applied by the prior art spraying devices has been impaired over the course of time which meant that the signal/response delay times had to be readjusted and reprogrammed by tedious manual operations.
For these reasons, similar problems may also arise in the paint feed lines running to the spraying device. These paint feed lines usually contain a feed pump which direct the paint through a return-circuit bridging the pump when the spraying device is switched off so that, when the paint needle-valve in the spraying device is opened, the required pressure is immediately available. The return-circuit bridging the pump includes a flow control valve which opens automatically when the paint needle-valve closes and closes when the paint needle-valve opens. It has hitherto been customary to use a pressure relief valve for this purpose. In order to avoid excessive or deficient pressure in the paint feed lines, it was previously desirable to switch the flow control valve in the return circuit which separate individual signals at times accurately matching the opening and closing of the paint needle-valve. However, the adjusted switching times for the return circuit would not correspond to the actual conditions if ever the response behavior of the spraying device were to change.